The present invention relates to vector modulators, and more particularly, to wideband vector modulators that use gallium arsenide integrated circuits and that sum outputs of a plurality of quadrature-phase-shift-key (QPSK) modulator elements that are each controlled by two digital inputs and a single local oscillator.
U.S. Pat. No. 5,237,292 issued to Chethik and assigned to the assignee of the present invention discloses a quadrature amplitude modulation system where the present vector modulator may be employed. In the system described in the Chethik patent, digital signals are converted to phase and amplitude altered, periodic, analog signals and that are coupled to an output link. The system is adaptive and includes a plurality of simple quadrature phase shift keying modulators, each modulator having a plurality of controlling digital inputs, the state of which determines which of a plurality of phase displaced signals will be output. A local oscillator provides a periodic sinusoidal signal to each QPSK modulator. Summing circuits combine the outputs of the modulators to produce a constellation of phase and amplitude-displaced output sinusoidal signals. A processor/mapper combination enable conversion of a first set of digital inputs to a different set of digital outputs in accordance with a control input. Thus, the processor enables the alteration of the constellation of outputs in accordance with a control input, which may be indicative of the condition of a transmission facility.
The Chethik patent thus discloses a quadrature amplitude modulation system that employs quadrature-phase-shift-key vector modulators. However, the Chethik patent does not disclose or suggest the use of GaAs microwave monolithic integrated circuits to implement the quadrature-phase-shift-key modulators.
Other patent references generally disclose vector modulators, and include U.S. Pat. No. 4,168,397 issued to Bradley, U.S. Pat. No. 4,464,767 issued to Bremer, U.S. Pat. No. 4,571,549 issued to Lods et al., U.S. Pat. No. 4,930,141 issued to Ohmagari, U.S. Pat. No. 4,843,351 issued to Edwards et al., and U.S. Pat. No. 4,999,590 issued to Verdot.
It is therefore an objective of the present invention to provide for a quadrature amplitude modulation system that employs gallium-arsenide-based vector modulators. It is a further objective of the present invention to provide for wideband vector modulators that are implemented using gallium ,arsenide integrated circuits. It is yet another objective of the present invention to provide for a wideband gallium arsenide vector modulator wherein outputs of a plurality of quadrature-phase-shift-key modulator elements are each controlled by two digital inputs and a single local oscillator.